Roger, I've been working with homegrown Marquette grapes for 5 years. I finally hit on a good strategy this year. I added the equivalent of 1g of pot bicarb per liter of finished wine to my must. This took the TA from 12 to 10 and the pH from 3.1 to 3.4. I then fermented with 71b yeast. It is now thru MLF and the pH is 3.52 and the TA is 6.9. It's ready to go into the barrel and tasting great. If you're already through MLF, add pot bicarb depending on where your pH and TA is before also doing a cold stab. Go slowly with the pot bicarb additions, as the pH can jump in a hurry. I start with half as much as calcs call for. And taste as you go. Too much pb will provide off flavors.